1. Field of the Invention
The present invention relates to a fuel cell system including a fuel cell stack formed by stacking a plurality of electrolyte electrode assemblies and separators. Each of the electrolyte electrode assemblies includes a pair of electrodes, and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes an anode, a cathode, and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane (proton exchange membrane). The membrane electrode assembly is interposed between separators. The membrane electrode assembly and the separators make up a fuel cell.
Generally, a predetermined number of fuel cells (membrane electrode assemblies and separators) are stacked together to form a fuel cell stack. In the fuel cell stack, a fuel gas such as a hydrogen-containing gas is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane which is humidified to a desirable extent, and the electrons flow through an external circuit to the cathode, creating a DC electric current. An oxygen-containing gas such as air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen gas to produce water.
Fuel cell systems utilizing the fuel cell stack in vehicle applications are known in the art. Referring to FIG. 13, a fuel cell system 1 includes a fuel cell stack 2. A fuel gas supply unit 3 for supplying a fuel gas such as a hydrogen-containing gas to the fuel cell stack 2, an oxygen-containing gas supply unit 4 for supplying an oxygen-containing gas such as air to the fuel cell stack 2, and a coolant supply unit 5 for supplying a coolant to the fuel cell stack 2 are provided.
The fuel gas supply unit 3 includes a fuel tank 6. The fuel tank 6 and a fuel gas flow passage (not shown) of the fuel cell stack 2 are connected through a fuel gas supply passage 7. A fuel gas supply pump 8 is provided in the fuel gas supply passage 7. The fuel gas supply pump 8 is connected to a pump motor 9.
The oxygen-containing gas supply unit 4 includes an oxygen-containing gas supply passage 10 and an oxygen-containing gas discharge passage 11 connected to an oxygen-containing gas flow passage (not shown). An inlet filter 12 and an oxygen-containing gas supply pump 14 are provided in the oxygen-containing gas supply passage 10. The oxygen-containing gas supply pump 14 is connected to a pump motor 13. The oxygen-containing gas discharge passage 11 is connected to a gas discharge unit 16.
A coolant supply unit 5 includes a circulation passage 17 connected to a coolant flow passage (not shown) of the fuel cell stack 2. A coolant supply pump 19 and a radiator 20 are provided in the circulation passage 17. The coolant supply pump 19 is connected to a pump motor 18. The circulation passage 17 includes a bypass passage 21 in parallel to the radiator 20.
A valve 22 is disposed in the bypass passage 21. The valve 22 performs a switching operation for the coolant to flow through the radiator 20 or not to flow through the radiator 20.
For example, the fuel cell stack 2 is placed in an underfloor area of the vehicle. The fuel cell system 1 is controlled by a PCU (power control unit) in a front box, for example, to drive motors 9, 13, 18 to supply the fuel gas, the oxygen-containing gas, and the coolant to the fuel cell stack 2, using the pumps 8, 14, 19.
In the conventional technique, the fuel cell stack 2 is placed under the vehicle, and the pumps 8, 14, 19 require the dedicated motors 9, 13, 18, respectively. Therefore, the overall size of the fuel cell system 1 is considerably large, the structure is complicated, and the production cost is high.
In the case the fuel cell system is used in a vehicle application, as shown in FIG. 14, for example, the fuel cell stack 2 is placed in an underfloor area 24 of a vehicle body 23. A coolant supply pump (not shown) is placed in the underfloor area 24. Further, an oxygen-containing gas supply pump 14 is placed in a front box 25 of the vehicle body 23, and a fuel tank 6 is placed in a rear box 27 of the vehicle body 23.
In the conventional technique, the fuel cell stack 2 is placed in the underfloor area 24, the oxygen-containing gas supply pump 14 is placed in the front box 25, and the fuel tank 6 is placed in the rear box 27. Therefore, pipes for connecting auxiliary equipment such as the oxygen-containing gas supply pump 14 and the fuel tank 6 to the fuel cell stack 2 are considerably long. The space in the overall fuel cell system 1 is not utilized efficiently.
Since the pipes as flow passages of the oxygen-containing gas and the fuel gas are long, pressure losses of the fluids in the pipes are large. Therefore, large energy losses occur in the auxiliary equipment, and the power generation performance in the overall fuel cell system is decreased.
Since the pipes are long, responsiveness to load changes is bad, and piping layout is complicated. Thus, it is difficult to use a turbo charger system which is operated by off-gas. Therefore, the fuel cell system 1 can not be used in a wide variety of applications.